docs: add saturday_delivery for bpost (#37)

src/api-reference/06.shipments.md

@@ -30,7 +30,7 @@ used when creating shipments.
 #### 2. Mailbox package
 
 This package type is only available on <DataType type="platform" id="1" />
-and <DataType type="platform" id="3" /> for NL shipments that fit into a
+and <DataType type="platform" id="2" /> for NL shipments that fit into a
 mailbox. It does not support additional options.
 
 ::: note
@@ -82,7 +82,7 @@ This is the standard delivery type.
 #### 3. Evening
 
 This option is only available on <DataType type="platform" id="1" />
-and <DataType type="platform" id="3" /> for certain NL addresses. It allows a
+and <DataType type="platform" id="2" /> for certain NL addresses. It allows a
 Customer/Consumer to have their package delivered in the evening on the
 specified delivery date.
 
@@ -145,9 +145,14 @@ and signature.
 #### age_check
 
 Only available on <DataType type="platform" id="1" />
-and <DataType type="platform" id="3" />. The Customer/Consumer must sign for the
+and <DataType type="platform" id="2" />. The Customer/Consumer must sign for the
 package and only receive it when he is at least 18 years.
 
+#### saturday_delivery
+
+Only available on <DataType type="platform" id="3" /> and carrier bpost. An additional fee is paid
+for delivery on saturdays.
+
 ### 6.A.4 Examples
 
 ::: expand Pickup
@@ -471,6 +476,7 @@ Authorization: bearer BASE64_ENCODED_API_KEY
         "options": {
           "package_type": 1,
           "signature": 0,
+          "saturday_delivery": 1,
           "insurance": {
             "amount": 0,
             "currency": "EUR"